This invention relates generally to the field of combustion and more particularly to combustion in a porous wall furnace.
In a typical process for heating and/or melting a charge such as glass or metal, certain undesirable features in the process will inevitably occur such as conductive heat loss from the wall of the furnace and corrosion in the furnace wall caused by corrosive gases in the furnace.
Considerable amount of work has been done to address the concerns for overcoming these undesirable features. For example, in order to reduce the loss of heat from the furnace wall during heating and/or melting of the charge, more insulation may be provided. To reduce the corrosion of the refractory walls, certain special refractory materials may be used. Furthermore, certain techniques for premixing the fuel and oxidant before injecting gases into the furnace allow combustion to take place relatively rapidly in spite of low gas injection velocity. However, to the most part, combustion in industrial furnaces in the present state of the art nevertheless involves some aspects of conductive heat loss from the furnace and corrosion caused by corrosive gases, or some other undesirable effects.
For example, in U.S. Pat. No. 5,609,481, a stratified atmosphere combustion is disclosed wherein both fuel and oxidant are introduced very closely into the furnace. In this case, a charge proximal stratum is established between the charge and the combustion gas emanating from one or more burners that are oriented above the charge. The charge-proximal stratum has a different oxidative effect on the charge than does the combustion gases. This method requires both fuel and oxidant to be introduced at very low velocities into a furnace, which tends to cause the fuel and oxidant mixing to be very slow, resulting in poor combustion, like sooty flame.
In another example, U.S. Pat. No. 5,076,779 provides for a segregated zoning combustion. This combustion method separates the oxidant mixing zones and fuel reaction zones in a combustion zone to dilute oxidant and combust fuel under conditions which reduces the NOx formation. This method requires that the oxidant be injected in high velocity and diluted with the furnace gas, thus requiring a high oxygen supply pressure.
Accordingly, it is an object of this invention to provide a furnace system that will enable effective heating and/or melting of a charge so that the heat loss of the system is dramatically reduced, reducing the corrosion of the refractory walls and injecting the oxidant at a low velocity while mixing the oxidant with the fuel or furnace gases at a fast rate.
It is an object of the invention to provide a method for combustion that reduces the heat loss in the combustion process.
It is another object of this invention to provide a method for combustion that reduces the corrosion in the refractory walls of the furnace.
It is yet another object of this invention to provide a method for combustion that introduces an oxidant at a very low velocity, and which mixes the fuel or furnace gas at a fast rate.
This invention is directed to a method for carrying out combustion in a furnace having porous walls. The furnace has a combustion zone containing an atmosphere of furnace gases. A low velocity oxidant stream is injected through at least one oxidant injection side of the porous walls into the combustion zone. A fuel stream is injected through at least one fuel injection side directed toward the oxidant injection side in the combustion zone. Furnace gases are separately mixed with at least an oxidant stream and a fuel stream to produce at least a separate diluted oxidant-furnace gas mixture and a fuel furnace gas mixture. The oxidant-furnace gas mixture is mixed with the fuel-furnace gas mixture to create a diluted fuel-oxidant-furnace gas mixture.
In an alternative embodiment, a low velocity fuel stream is injected through at least one fuel injection side of the porous walls into the combustion zone, and the oxidant stream is injected through at least one oxidant injection side directed toward the fuel injection side of the combustion zone.